In the field of working machines such as an excavator, a plurality of cameras are placed on the rear side and the lateral side of a vehicle body, and an image captured by each of the cameras is shown as a single camera image on a monitor in a cab of the working machine so that an operator can visually recognize an obstacle present around the vehicle body. Further, as disclosed in Patent Literature 1, images captured by the respective cameras are transformed into upper viewpoint images, the transformed images are synthesized to generate a bird's eye image, and the bird's eye image is displayed on a monitor so as to simultaneously monitor the surroundings of a vehicle body.
Further, there is a display device such as a monitor that has a function for performing calibration (adjustment processing) on an image to be displayed. For example, Patent Literature 2 is a document regarding calibration in a touch panel and describes one capable of performing a calibration mode by detecting the turning-on of power to an electronic device provided with a touch panel or touch to the touch penal by a predetermined number of times within a certain time from a reset operation even when an incorrect reference point is set, or when a resistance value of the touch penal largely changes to cause large displacement between the position of a display screen and a touch panel input position and touch of an operation button cannot be detected.